Off-Balance Sheet Arrangements (Details) (USD $) In Millions, unless otherwise specified	Nov. 16, 2011 extensions
Off-Balance Sheet Arrangements Disclosure [Abstract]
Contingent put option created pursuant to securities issuance agreement and reinsurance agreement, value	$ 350.0
Number of mandatory extensions	4

Contingent put option created pursuant to Securities issuance agreement entered by company and certain operating subsidiaries and reinsurance agreement entered by certain foreign insurance and reinsurance subsidiaries.

No definition available.

Name:	xlgroup_ContingentPutOptionCreatedPursuantToSecuritiesIssuanceAgreementAndReinsuranceAgreement
Namespace Prefix:	xlgroup_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant